Voltage stabilizer and reference circuit therefor



April 3, 1956 R. E. ANDERSON 2,740,936

VOLTAGE STABILIZER AND REFERENCE CIRCUIT THEREFOR Filed Dec. 30, 1953Ihven tor: Ray E. An derson,

y His Attorney.

United States Patent'O VOLTAGE STABILIZER AND REFERENCE CIRCUIT THEREFORRay E. Anderson, 'Fort Wayne, Ind., assignor to General ElectricCompany, a corporation of New York Application December 30, 1953, SerialNo. 401,314

19 Claims. (Cl. 323-66) This invention relates to voltage stabilizingsystems and to thereference circuits for such systems, and moreparticularly to an alternating-current voltage stabilizer utilizing abridge-type reference circuit.

There are many applications which require an alterhating-current voltagemore stable than the available line voltage. In the past, manyalternating-current voltage stabilizing systems have been devised, thesesystems generally using a reference circuit and adjusting the outputvoltage in response to deviations of the input voltage from the ref encevalue. Bridge circuits have been used for the refererence, however, suchcircuits have been severely affected by temperature changes and driftcaused primarily by theme of rectifiers for. demodulation in the directpath of the reference signal and the random drift of directcurrentdevices such as glow tubes.

It is desirable that magnetic amplifiers be utilized in voltagestabilizing systems since they are much more sturdy than vacuum tubeamplifiers. The use of magnetic amplifiers however, requires that a lowfrequency or direct-current control signal be provided by the referencecircuit. Furthermore, since an alternating current input and output isinvolved, it is necessary that the reference circuit detect deviationsin the input voltage from the preselected desired value and convertthese deviationsinto a direct-current signal suitable for controlling amagnetic amplifier. It is further. desirable that the system not beeffected by ambient temperature changes and that reference drift be heldto a minimum. It is also desirable that rectifiers be eliminated fromthe direct path of the reference signal in closed loop feedback systemsand that the system be capable of operation over a wide frequency range.

It is therefore an object of this invention to provide an improvedvoltage stabilizing system incorporating the desirable features setforth above.

Another object of this invention is to provide an improved referencecircuit incorporating the desirable features set forth above.

Further objects and advantages of this invention will become apparentand the invention will be better understood by reference to thefollowing description and the accompanying drawing; and the features ofnovelty which characterize this invention will be pointed out withparticularity in the claims annexed to and forming a part ofthis'specification.

This invention in its broadest aspects provides a bridgetype referencecircuit utilizing both fixed linear and nonlinear impedance elements.This bridge circuit has two fixed linear impedance legs and twonon-linear impedance legs with a voltage proportional to the inputvoltage being applied to the bridge to cause circulating current thereinand another voltage derived from an independent circuit also beingapplied to the bridge. Since the impedance of the non-linear legs is afunction of the value of the circulating current, the balance orunbalance of the bridge is dependent upon the applied voltage. The othervoltage applied to the'bridge provides an output during bridge 2 Funbalance, with a magnitude substantially proportional to the deviation.This output signal can therefore be utilized to control a magneticamplifier which in turn provides the stabilized output voltage.- Thus,the sensing, comparing, reference-and demodulating functions are allperformed by this static network.

In the drawing:

Fig. 1 is a schematic illustration of an improved closed loop feedbackalternating-current voltage stabilizing system according to thisinvention incorporating my improved reference circuit; and

Fig. 2 is a schematic illustration of a modified form of the referencecircuit.

Referring now to Fig. 1, the alternating-current voltage to bestabilized is applied across input terminals 1 and 2, terminal 2 beingconnected to a common bus 3 to which one output terminal 4 is connected.Another output terminal 5 is provided with the autotransformer 6 beingconnected across output terminals 4 and 5.

Reference circuit 16 is of the bridge type with nonlinear resistanceelements 11 being arranged in two opposite legs and with fixed linearresistance elements 1 2 being arranged in the-other two opposite legs.Non-linear resistance elements 11 may be conventional tungsten filamentlamps known for their non-linear current characteristic and linearresistance elements 12 may be high quality resistors formed of materialsuch as Nichrome or constantan. Transformers 13 are provided withtheir-secondary windings 14 respectively connected in series with linearresistance elements 12 and with their primary windings 15 connected inparallel across the output terminals 4 and'S. it will now be seen that avalue of an alternatingcurrent voltage proportional to the voltageacross output terminals 4 and 5 is applied to the fixed linear legs ofthe bridge of reference circuit 10, thus causing circulating current toflow in the entire bridge circuit.

In order to supply a direct-current voltage for the bridge referencecircuit 10 so that a direct-current output may be provided thereby, abridge rectifier circuit 17 has its output connected to opposite corners18 of bridge reference circuit 10. A variable resistance19,-potentiometer 20 and resistance 21 are connected in series with thesliding element 23 of variable resistance 19 being connected to theautotransformer tap 8 in the output circuit and the extreme end ofresistance 21 beingconnected to output terminal 4. It is thus apparentthat the voltage across the resistance circuit including resistances 19,20 and 21 is proportional to the output voltage across terminals 4 and5. The input to rectifier 17 is taken across sliding element 24 ofpotentiometer 20 and the common bus 3. It is thus seen that a small,constant direct-current voltage is applied to opposite corners 18 ofbridge reference circuit 10. The other two opposite corners 25constitute the output terminals of the bridge reference circuit 10 andare connected to control windings of the magnetic amplifiers of theclosed-loop feedback voltage stabilizer system which will be hereinafterdescribed.

It will now be seen that the voltage. rises and drops caused by thecirculating alternating-current in the bridge reference circuit 10completely cancel in the bridge and act to adjust the resistances ofthenon-linear resistance elements 11, the resistances of theseelementsbeing dependent upon the current flow therethrough, which inturn depends upon the voltages'applied by the transformers 13. It isthus seen that. the reference bridge circuit 10 can be balanced by meansof resistors 12 so that no directcurrent voltage appears across outputterminals 25 at a desired reference voltage. Under these conditions, thealternating-current voltage applied by transformers 13 will result inthe resistance of non-linear resistance elements 11 being such thatthebridge is completely balanced.

Nowassuming that the'output voltage across theoutput terminals 4 and 5of the voltage stabilizing system tends to increase thus producing aproportional increase in the voltage applied by transformers 13. Thiswill result in a corresponding increase in the circulatingalternating-current in the reference bridge circuit thus producing acorresponding change in the resistance of non-linear elements 11. Thiscauses the bridge to be unbalanced and produces a direct-current voltageacross output terminals with a polarity des termined by the polarity ofthe voltage applied across corners 18 by the rectifier circuit 17. Asthe voltage across output terminals 4 and 5 tends to deviate further inthe same direction, the direct-current voltage appearing across outputterminals 25 of bridge circuit 10 will show a further increase.

Assuming that the voltage across output terminals 4 and 5 decreased fromthe selected value, the voltage applied to the reference bridge circuitby the transformers 13 would decrease thus causing the circulatingalternat ing-current in the reference bridge circuit 10 to decrease anda resultant change in the opposite direction in the resistance ofnon-linear resistance elements It. This again unbalances the bridgeproducing a direct-current voltage across output terminals 25 with thepolarity now being reversed from that existing when the output voltageacross output terminals 4 and 5 was above the preselected value. It isthus seen that the direct-current voltage across output terminals 25 ofbridge reference 10 is a direct-current voltage substantiallyproportional to the deviation of the alternating-current output voltageacross output terminals 4 and 5 from the preselected value with thepolarity being dependent upon the direction of the deviation from thepre-selected value. Thus, it is seen that this bridge circuit acts as ademodulator as well as a reference.

In order to correct the deviation in output voltage across terminals 4and 5, output terminals 25 of the bridge reference circuit 10 areconnected to the directcurrent control windings 26 and 27 of push-pullmagnetic amplifiers 28 and 29. The power windings 30 and 31 of magneticamplifier 28 are respectively connected between bus 3 and bridgerectifier 32 and power windings 33 and 34 of magnetic amplifier 29 arerespectively connected between bus 3 and bridge rectifier 35. Bridgerectifiers 32 and 35 are connected for energization from the outputvoltage across output terminals 4 and 5 by conductors 36 and 37; andtheir opposite corners 38 and 39, and 4t) and 41, are respectivelyconnected to direct current control windings 42 and 43 of outputmagnetic amplifier 44.- Power windings 45 and 46 of output magneticamplifier 44 are connected between input terminal 1 and a tap 7 on theautotransformer 6 in the output circuit with rectifiers 58 and 49 beingrespectively interposed in series therewith. Resistor 56 is placed toprotect rectifiers 48 and 49 during transient conditions.

It will now be seen that a direct-current signal of a given polarityappearing across output terminals 25 of bridge reference circuit 10 isapplied to control windings 26 and 27 of a push-pull magnetic amplifier2-8 and 29. This direct current signal will therefore tend to saturatethe cores of the magnetic amplifiers 28 and 29 respectively in a givendirection thus increasing or decreasing, dependent upon the polarity ofthe signal across output terminals 25 of reference bridge circuit 10,the current flowing in control windings 42 and 43 of output magneticamplifier 44. This of course through the power windings 45 and 46controls the voltage applied across the output circuit and the outputterminals 4 and 5.

It is now seen that this improved circuit provides analternating-current voltage stabilizing system which can detect on thebasis of the R. M. S. value of the alternating current voltage to becontrolled; which provides a direct-current signal for controlling themagnetic amplifiers; and which does not have any rectifiers-in thedirect path of the reference signal. It will also be apparent that thereference circuit is not subject to changes in ambient temperature sincesuch changes will have a uniform effect upon the bridge referencecircuit and will not cause unbalance, and it will also be readilyapparent that the device is capable of operation over a relatively widerange of input frequency.

'It will be readily understood that a single transformer having oneprimary winding and two secondary windings may be utilized instead ofthe two transformers 13 of Fig. 1. It will also be readily understoodthat impedances other than resistances may be used for the fixed linearand non-linear legs of bridge reference circuit 10.

Referring now to Fig. 2, there is shown an alternative form of referencecircuit utilizing a filter network for impressing an alternating-currentvoltage upon the bridge rather than the transformers 13 of Fig. 1. Here,nonlinear resistance elements 11 again form two opposite legs of thebridge and linear resistance elements 50 form the other two oppositelegs of the bridge. The direct-current input to the bridge is applied toopposite corners 18 and the output is taken from the other two oppositecorners 25. Here, serially connected filter capacitors 51 and 52 areconnected across correspond ing ends of the non-linear resistanceelements 11 while another pair of serially connected filter capacitors53 and 54 are connected across the other two corresponding ends of thenonlinear resistance elements 11. The alternating-current voltage isapplied to terminals 55 connected respectively between the mid pointsbetween the capacitors 51 and 52, and 53 and 54 respectively. It may befound that the filter network means of introducing the alternatingcurrent to the reference bridge circuit shown in Fig. 2 is moredesirable if higher frequencies are used.

It will be readily apparent that the reference circuit 10 to Fig. 1 orthe reference circuit of Fig. 2 may be used independently of the voltagestabilizer system of Fig. 1 in any application where a direct-currentreference or modulated frequency signal is desired. Also it will bereadily apparent that an alternating-current signal may be appliedacross the corners 18 of the bridge reference circuit to obtain analternating current output.

While I have described particular embodiments of this invention, furthermodifications and improvements will occur to those skilled in the art. Idesire it to be understood therefore that this invention is not limitedto the form shown and I intend in the appended claims to cover allmodifications which do not depart from the. spirit and scope of thisinvention.

I claim:

1. A reference circuit for supplying a signal proportional to thedeviation of an alternating-current voltage from a preselected valuecomprising a bridge circuit having non-linear impedance elements in apair of opposite legs and fixed linear impedance elements in the otherpair of opposite legs, connections for impressing a voltage on twoopposite corners of said bridge circuit, output terminals connected tothe other two opposite corners of said bridge circuit, and means forimpressing said alternating-current voltage respectively on one of saidpair of opposite legs of said bridge circuit thereby producingcirculating alternating-current therein, said bridge circuit beingbalanced at said preselected alternating-current voltage value with theimpedance of said non-linear impedance elements varying in response tovariations in said alternating-current voltage thereby producing avoltage across output terminals substantially proportional to thedeviation in the said alternating current voltage from preselectedvalue.

2. A reference'circuit for supplying a signal proportional to andindicativeof the deviation of analternating-current voltage from apreselected value comprising a bridge circuit having non-linearimpedance elements in a pair of opposite legs and fixed linear impedanceelements in the other two opposite legs, connections for impressing adirect-current voltage on two opposite corners of said bridge circuit,output terminals connected to the other two opposite corners of saidbridge circuit, and means for impressing said alternating-currentvoltage respectively on one of said pair of opposite legs of directionof said deviation.

3. A reference circuit for supplying a signal proportional to andindicative of the deviation of an alternating-current voltage from apreselected value comprising a bridge circuit having non-linearresistance elements in two opposite legs and fixed linear resistanceelements in the other two opposite legs, connections for impressing adirect-current voltage derived from said alternating-current voltage ontwo opposite corners of said bridge circuit, output terminals connectedto the other two op posite corners of said bridge circuit, and means forimpressing said alternating-current voltage on said other two oppositelegs of said bridge circuit thereby producing circulatingalternating-current therein, said bridge circuit being balanced at saidpreselected alternating-current voltage value with the resistance ofsaid non-linear resistance elements varying in response to variations insaid alternating-current voltage thereby producing a directcurrentvoltage across said output terminals substantially proportional to thedeviation of the said alternating-current voltage from said preselectedvalue and polarized to indicate the direction of said deviation.

4. A reference circuit for supplying a signal proportional to andindicative of the deviation of an alternatingcurrent voltage from apreselected value comprising a bridge circuit having non-linearresistance elements in two opposite legs and fixed linear resistanceelements in the other two opposite legs, a rectifier having its inputadapted to be connected for energization from said alternating-currentvoltage and having its output connected across two opposite corners ofsaid bridge circuit, output terminals connected to the other twoopposite corners of said bridge circuit, and means for impressing saidalternating-current voltage on said other two opposite legs of saidbridge circuit thereby producing circulating alternating-currenttherein, said bridge circuit being balanced at said preselectedalternating-current voltage value with the resistance of said non-linearresistance elements varying in response to variations in saidalternating-current voltage thereby producing a direct-current voltageacross said output terminals substantially proportional to the deviationof said alternating-current voltage from said preselected value andpolarized to indicate the direction of said deviation.

5. A reference circuit for supplying a signal proportional to thedeviation of an alternating-current voltage from a preselected valuecomprising a bridge circuit having non-linear resistance elements in twoopposite legs and fixed linear resistance elements in the other twoopposite legs, connections for impressing voltage on two oppositecorners of said bridge circuit, output terminals connected to the othertwo opposite corners of said bridge circuit, and transformer meanshaving secondary Windings in each of said other two opposite legs andadapted to be energized from said alternating-current voltage forimpressing said alternating-current voltage on said other two oppositelegs of said bridge circuit thereby producing circulatingalternating-current therein, said bridge circuit being balanced at saidpreselected alternating-current voltage value with the resistances ofsaid non-linear resistance elements varying in response to variations in6 said alternating-current voltage thereby producing a'voltage acrosssaid output terminals substantially proportional to the deviations ofsaid alternating-current voltage from said preselected value.

6. A reference circuit for supplying a signal proportional to andindicative of-the deviation ofan alternatingcurrent voltage from apreselected value comprising a bridge circuit having non-linearresistance elements in two opposite legs and fixed linear resistanceelements in the other two opposite legs, connections for impressing adirect-current voltage derived from said alternating-current voltage ontwo opposite corners of said bridge circuit, output terminalsconnected'to the other two output terminals of said bridge circuit, andtransformer means having secondary windings ineach of said other twoopposite legs and adapted to be energized from said alternating-currentvoltage for impressing said alternatingcurrent voltage on said other twoopposite legs of said bridge circuit thereby producing circulatingalternatingcurrent therein, said bridge circuit being balanced at saidpreselected alternating-current voltage value with the resistances ofsaid non-linear resistance elements varying in response to variations insaid alternating-current voltage thereby producing a direct-currentvoltage across said output terminals substantially proportional to thedeviations of said alternating-current voltage from said preselectedvalue and polarized to indicate the direction of said deviation.

7. A reference circuit for supplying a signal proportional to thedeviation of an alternating-current voltage from a preselectedvaluecomprising a bridge circuit having non-linear resistance elements in twoopposite legs and fixed linear resistance elements in the other twoopposite legs, connections for impressing a voltage on two oppositecorners of said bridge circuit, output terminals connected to the othertwo opposite corners of saidbridge circuit, and filter networks adaptedto impress said alternating-current voltage across said non-linearresistance elements thereby producingalternating-current in said bridgecircuit, said bridge circuit being balanced at said I preselectedalternating-current voltage value with the resistances of saidnon-linear resistance elements varying in -response to variations insaid alternating-current voltage thereby producing a voltage across saidoutput terminals substantially proportional to the-deviation of saidalter nating-current voltage from said preselected value.

8. A reference circuit for supplying a signal proportional to andindicative of the deviation of an alternatingcurrent voltage from apreselected value comprising a bridge circuit'having non-linearresistance elements in two opposite legs and fixed linear resistanceelements in the other two opposite legs, connections for impressing adirect-current voltage derived from said alternating-current voltage ontwo opposite corners of said bridge circuit, output terminals connectedto the other two opposite corners of said bridge circuit, and filternetworks adapted to impress said alternating-current voltage across saidnon-linear resistance elements thereby producing alternating-current insaid bridge circuit, said bridge circuit being balanced at saidpreselected alternating-current voltage value with the resistances ofsaid non-linear resistance elements varying in response to variations insaid alternating-current voltage thereby producing a directcurrentvoltage across said output terminals substantially proportional to thedeviation of said alternating-current voltage from said preselectedvalue and polarized to indicate the direction of said deviation.

9. A reference circuit for supplying a signal proportional to andindicative of the deviation of an alternatingcurrent voltage from apreselected value comprising a bridge circuit having non-linearresistance elements in two opposite legs and fixed linear resistance,elements in'the other two opposite legs, connections for impressing .adirect-currentvoltage derived from said alternating-current voltage ontwo opposite corners of said bridge circuit, outavenues put terminalsconnected to the other two opposite corners of said bridge circuit, andfilter capacitor respectively having one side connected to the ends ofsaid non-linear resistance elements adapted to have their opposite endsconnected to said alternating-current voltage for impressing saidalternating-current voltage acrosssaid nonlinear resistance elementsthereby producing alternatingcurrent in said bridge circuit, said bridgecircuit being balanced at said preselected alternating-current voltagevalue with the resistances of said non-linear resistance elementsvarying in response to variations in said alter hating-current voltagethereby producing a direct-current voltage across said output terminalssubstantially proportional to the deviation of said alternating-currentvoltage from said preselected value and polarized to indicate thedirection of said deviation.

10. A closed loop feedback alternating-current voltage stabilizer systemcomprising a bridge circuit having non-linear impedance elements in twoopposite legs and fixed linear impedance elements in the other twoopposite legs, an output circuit, an amplifier having its outputconnected to energize said output circuit, its two opposite corners ofsaid bridge circuit being adapted to be connected to a source ofvoltage, the other two opposite corners of said bridge circuit beingconnected to the control element of said amplifier, and means forimpressing a voltage taken from said output circuit on said other twoopposite legs of said bridge circuit thereby producing circulatingalternating-current therein, said bridge circuit being balanced at apreselected alternating current output voltage value with the impedanceof said non-linear impedance elements varying in response to variationsof said alternating-current output voltage thereby producing a voltageacross said amplifier control element substantially proportional to thedeviation of said alternating-current output voltage from saidpreselected value.

11. A closed loop feedback alternating-current voltage stabilizer systemcomprising a bridge circuit having non-linear impedance elements in twoopposite legs and fixed linear impedance elements in the other twoopposite legs, an output circuit, an amplifier having its outputconnected to energize said output circuit, a rectifier hav' ing itsinput connected for energization from said output circuit and having itsoutput connected across two opposite corners of said bridge circuit, theother two opposite corners of said bridge circuit being connected to thecontrol element of said amplifier, and means for impressing a voltagetaken from said output circuit on said other two opposite legs of saidbridge circuit thereby producing circulating alternating-currenttherein, said bridge circuit being balanced at a preselectedalternating-current output voltage value with the impedance of saidnon-linear impedance elements varying in response to variations of saidalternating-current output voltage thereby producing a direct-currentvoltage across said amplifier control element substantially proportionalto the deviation of said alternating-current output voltage from saidpreselected value and polarized to indicate the direction of saiddeviation.

12. A closed loop feedback alternating-current voltage stabilizer systemcomprising a bridge circuit having non-linear resistance elements in twoopposite legs and fixed linear resistance elements in the other twoopposite legs, an output circuit, an amplifier having its outputconnected to energize said output circuit, a rectifier having its inputconnected for energization from said output circuit and having itsoutput connected across two opposite corners of said bridge circuit, theother two opposite corners of said bridge circuit being connected to thecontrol element of said amplifier, and transformer means havingsecondary windings in each of said other two opposite legs and beingconnected for energization from said output circuit for impressing said,alternatingcurrent output voltage on'said other two opposite legs ofsaid bridge circuit thereby producing circulating alternatingcurrenttherein, said bridge circuit being balanced at a preselectedalternating-current output voltage value with the resistance of saidnon-linear resistance elements varying in response to variations in saidalternating-current output voltage thereby producing a direct-currentvoltage across said amplifier control element substantially proportionalto the deviation of said alternating-current output voltage frompreselected value and polarized to indicate the direction of saiddeviation.

1?).- A closed-loop feedback alternating-current voltage stabilizersystem comprising a bridge circuit having non linear resistance elementsin two opposite legs and fixed linear resistance elements in the othertwo opposite legs, an output circuit, an amplifier having its outputconnected to energize said output circuit, two opposite corners of saidbridge circuit being adapted to be connected to a source of voltage, theother two opposite corners of said bridge circuit being connected to thecontrol element of said amplifier, and filter networks impressing avoltage taken from said output circuit across said non-linear resistanceelements thereby producing alternating-current in said bridge circuit,said bridge circuit being balanced at a preselected alternating-currentoutput voltage value with the resistance of said non-linear resistanceelements varying in response to variations in said alternating-currentoutput voltage thereby producing voltage across said amplifier controlelement substantially proportional to the deviation of saidalternatingcurrent output voltage from said preselected value.

14.- A closed-loop feedback alternating-current voltage stabilizersystem comprising a bridge circuit having non-linear resistance elementsin two opposite legs and fixed linear resistance elements in the othertwo opposite legs, an output circuit, an amplifier having its outputconnected to energize said output circuit, a rectifier having its inputconnected for energization from said output circuit and having itsoutput connected across two opposite corners of said bridge circuit, theother two opposite corners of said bridge circuit being connected to thecontrol element of said amplifier, and filter networks impressing avoltage taken from said output circuit across said non-linear resistanceelements thereby producing alternating-current in said bridge circuit,said bridge circuit being balanced at a preselected alternating-currentoutput voltage value with the resistance of said non-linear resistanceelements varying in response to variations in said alternating-currentoutput voltage thereby producing a direct-current voltage across saidamplifier control element substantially proportional to the deviation ofsaid alternating-current output voltage from said preselected value andpolarized to indicate the direction of said deviation.

15. A closed-loop feedback alternating-current voltage stabilizingsystem comprising a bridge circuit having nonlinear resistance elementsin two opposite legs and fixed linear resistance elements in the othertwo opposite legs, an output circuit, an amplifier having its outputconnected to energize said output circuit, a rectifier having its inputconnected for energization from said output circuit having its outputconnected across two opposite corners of said bridge circuit, the othertwo opposite corners of said bridge circuit being connected with controlelements of said amplifier, and filter capacitors respectively havingone side connected to one end of said non-linear resistance elements andhaving their other ends connected to said output circuit for impressinga voltage from said output circuit across said non-linear resistanceeiements thereby producing alternating-current in said bridge circuit,said bridge circuit being balanced at a preselected alternating-currentoutput voltage value with the resist ance of said non-linear resistanceelements varying in response to variations in the saidalternating-current output voltage thereby producing a direct-currentvoltage across said amplifier control element substantially proportionalto the deviation of said alternating-current output voltage from saidpreselected value and polarized to indicate the direction of saiddeviation.

16. A closed-loop feedback alternating-current voltage stabilizingsystem comprising a bridge circuit having non-linear resistance elementsin two opposite legs and fixed linear resistance elements in the othertwo opposite legs, an output circuit, a magnetic amplifier having itsoutput connected to energize said output circuit, a rectifier having itsinput connected for energization from said output circuit and having itsoutput connected across two opposite corners of said bridge circuit, theother two opposite corners of said bridge circuit being connected toenergize the control element of said magnetic amplifier, and means forimpressing a voltage taken from said output circuit on said two otheropposite legs of said bridge circuit, said bridge circuit being balancedat a preselected alternating-current output voltage value with theresistance of said non-linear resistance elements varying in response tovariations in said alternating-current output voltage thereby producinga direct-current voltage across said magnetic amplifier control elementsubstantially proportional to the deviation of said alternating-currentoutput voltage from said preselected value and polarized to indicate thedirection of said deviation.

17. A closed-loop feedback alternating-current voltage stabilizingsystem comprising a bridge circuit having non-linear resistance elementsin two opposite legs and fixed linear resistance elements in the othertwo opposite legs, an output circuit, a magnetic amplifier having itsoutput connected to energize said output circuit, a rectifier having itsinput connected for energization from said output circuit and having itsoutput connected across two opposite corners of said bridge circuit, theother two opposite corners of said bridge circuit being connected toenergize the control element of said magnetic amplifier, and transformermeans having secondary windings in each of said other two opposite legsof said bridge circuit and being connected for energizetion from saidoutput circuit for impressing said alternating-current voltage on saidother two opposite legs of said bridge circuit, said bridge circuitbeing balanced at a preselected alternating-current output voltage valuewith the resistance of said non-linear resistance elements varying inresponse to variations in said alterhating-current output voltagethereby producing a directcurrent voltage across said magnetic amplifiercontrol element substantially proportional to the deviation of saidalternating-current output voltage from said preselected value andpolarized to indicate the direction of said deviation.

18. A reference circuit for supplying a signal proportional to thedeviation of an alternating-current voltage from a preselected valuecomprising a bridge circuit having non-linear resistance elements in twoopposite legs and fixed linear resistance elements in the other twoopposite legs, connections for impressing a voltage on two oppositecorners of said bridge circuit, output terminals connected to the othertwo opposite corners of said bridge circuit, and means for impressingsaid alternating-current voltage on said other two legs of said bridgecircuit thereby producing circulating alternating current therein, saidbridge circuit being balanced at said preselected alternating-currentvoltage value with the resistance of said nonlinear resistance elementsvarying in response to variations in said alternating-current voltagethereby producing a voltage across said output terminals substantiallyproportional to the deviation of said alternating-current voltage frompreselected value.

19. A closed-loop feedback alternating-current voltage stabilizingsystem comprising a bridge circuit having nonlinear resistance elementsin two opposite legs and linear resistance elements in the other twoopposite legs, an out put circuit, a magnetic amplifier having itsoutput connected to energize said output circuit, a rectifier having itsinput connected for energization from said output circuit having itsoutput connected across two opposite corners of said bridge circuit, theother two opposite corners of said bridge circuit being connected to acontrol winding of a saturable core reactor, said saturable core reactorbeing connected for energization from said output circuit and having itsoutput connected to a control winding of said magnetic amplifier, andmeans for impressing a voltage taken from said output circuit on saidtwo other opposite legs of said bridge circuit thereby producingcirculating alternating-current therein, said bridge circuit beingbalanced at a preselected alternating-current voltage output value Withthe resistance of said non-linear resistance elements varying inresponse to variations in said alternating-current output voltagethereby producing a direct-current voltage across said magneticamplifier control winding substantially proportional to the deviation ofsaid alternating-current output voltage from said preselected value andpolarized to indicate the direction of said deviation.

References Cited in the file of this patent UNITED STATES PATENTS

